The invention relates generally to seismic exploration in and/or around a well drilled for hydrocarbon exploration and production. More specifically, the invention relates to methods and systems for acquiring seismic data in a marine environment.
Seismic data is collected to analyze subsurface properties and is particularly collected in connection with hydrocarbon exploration and production activities. Seismic data for analyzing subsurface formations may be collected on land or in water. Seismic data is acquired using explosive, vibratory, or impulsive seismoacoustic sources. An example of an impulsive seismoacoustic source is an air gun, which is used to release highly compressed air into water. Vibratory seismoacoustic sources are typically used on land when explosive seismoacoustic sources cannot be used. Seismoacoustic source signals are reflected by geological layers beneath the earth surface, and the reflections are detected by seismoacoustic receivers, such as geophones on land and hydrophones in water. The reflected signals are recorded and analyzed to derive an indication of the geology in the subsurface. Such indications may be used to assess the likelihood and location of potential hydrocarbon deposits.
Seismic data can be collected while drilling a well using measurement-while-drilling (MWD)/logging-while-drilling (LWD) seismic systems. Conventional MWD/LWD seismic systems, such as described in U.S. Pat. No. 6,308,137, are generally configured with a seismic tool located near the drill bit, where the seismic tool contains seismoacoustic receivers for recording the arrival of seismoacoustic source signals sent from seismoacoustic sources at the surface. In offshore operations, the surface seismoacoustic sources are typically air guns. If the well is vertical, then the drilling platform provides a suitable base for the air gun and its associated surface equipment. If the well is highly deviated or extended-reach, the air gun must be deployed from a vessel to locate it directly above the drill bit. The vessel has to be available during the entire drilling process since seismic data are acquired at specific intervals in the drilling operation. Maintaining a vessel and crew offshore adds considerable expense and complexity to seismic jobs.
From the foregoing, there continues to be a desire to improve the efficiency and cost of running seismic jobs in a marine environment.